Visual C++ :: How To Insert A String Right In The Middle Of Another String

I'm new to strings. I want to know how to insert a string right in the middle of another string.Is it possible to do that? for example my first random word is 12345678 and the 2nd random word is jimmy I would have to write .

This in my code uno.insert(4,dos); for jimmy to be printed in the middle of the first string,but what if my 1st random word is has more than 8 characters what would I do in that case?

Code:
cout << "type random word" << endl;
getline (cin , uno);
//greatavenue
cout <<"enter random word#2"<<endl;
getline (cin , dos);
//_coconut_

uno.insert(5,dos);
cout<<uno<<endl;
//great_coconut_avenue